The present invention relates to an apparatus for controlling a magnetic particle clutch for use of a vehicle in which an engine torque is transmitted by a magnetic particle clutch and a belt type continuously variable transmission, and particularly to an apparatus for protecting a belt type continuously variable transmission equipped with a magnetic particle clutch. This invention protects the belt by controlling the amount of torque transmitted through a magnetic particle clutch.
A continuously variable transmission includes a V-belt extending between driving and driven pulleys, with one or both of the pulleys being able to adjust the size of their respective V-shaped openings which hold the V-belt, thereby controlling the revolution ratio between the driving and driven pulleys. The size of the V-shaped opening is varied by changing the amount of pressure being fed into a hydraulic cylinder of either of the pulleys. Hence, the effective diameter of the pulley can be varied by changing the amount of pressure being fed into the hydraulic cylinder, thereby allowing for a continuously variable ratio of driving pulley effective diameter to driven pulley effective diameter. The V-shaped openings on the driving and driven pulleys are each defined by an area between a fixed portion of each pulley and a movable portion of each pulley, the size of the V-shaped opening being dependent upon the pressure inputted to the hydraulic cylinders, a hydraulic apparatus provides hydraulic pressure to each of the movable pulleys.
In the above-described belt type continuously variable transmission, some vehicles are equipped with a magnetic particle clutch which is provided between an engine and a continuously variable transmission. Such a magnetic particle clutch transmits an engine torque to a continuously variable transmission, in proportion to a magnitude of an electric current carried to a field coil. It is conventional that the magnitude of an electric current carried to a field coil is designed to be a fixed value after a magnetic particle clutch is engaged. Hence, the entire engine torque is transmitted to a belt type continuously variable transmission. When brake are applied quickly, a large amount of an engine torque is transmitted to the belt type continuously variable transmission, thereby resulting in slippage between the torque transmitting belt and the movable pulley.
In order to obviate the foregoing drawback, to the a large line pressure is supplied hydraulic cylinder for the movable pulley. Due Thus, the value of the line pressure exerted on the movable pulley in a direction that the movable pulley is approached to a torque transmitting belt, becomes large. According to the above countermeasure, the large line pressure is constantly supplied to a hydraulic cylinder. Hence, the power consumed by generating the high line pressure is large and the fuel efficiency is low. Further, when an unusually unusual large torque is transmitted to the continuously variable transmission, it is difficult to prevent slippage between the belt and the movable pulley.